1. Technical Field of the Invention
The present invention relates to a lobe mixer for jet flow in which a high-speed inner flow and low-speed outer flow are mixed and exhausted.
2. Description of the Related Art
Examples of an apparatus, high speed flow and low speed flow are mixed inside thereof, is an airplane engine which includes an afterburner. As shown in FIG. 1, an airplane engine 1 (jet engine) equipped with the afterburner includes: a fan 2 which takes in air; a compressor 3 which compresses the taken air; a combustor 4 which burns fuel by the compressed air; a turbine 5 which drives the fan 2 and compressor 3 by combustion gas of the combustor 4; and an afterburner 6 which burns the fuel again to increase a thrust force.
The afterburner 6 is constituted of: a flame holder 7 (flame holding unit) which has a triangular section and forms a circulation region X downstream to hold flame; a fuel nozzle 8 for spouting the fuel; and an ignition plug 9, and spouts the exhaust gas via an exhaust nozzle 12 through a liner 11 disposed inside an outer duct 10 to increase the thrust force.
Moreover, the air taken in by the fan 2 is branched into a core flow 14 which flows through the compressor 3, combustor 4, and turbine 5, and a bypass flow 13 (fan flow) which bypasses these components, and the flows are combined in a mixer (mixing unit) 15. It is to be noted that reference numeral 16 denotes a tail cone.
As shown in FIG. 2, the mixer 15 includes a guide wall (partition wall) whose transverse sectional shape is a waveform shape, the waveform shape is enlarged downstream, the fan flow 13 (solid line) and core flow 14 (broken line) are combined in a downstream end, and the circulation region X is formed on the downstream side of the mixer 15 in order to efficiently mix the flows. The mixer structured in this manner is generally called a lobe mixer.
The lobe mixer shown in FIG. 2 is also used as a mixture promoting apparatus for a purpose of reducing exhaust jet noise of a turbofan engine which does not include the afterburner. In this case, the mixer is not only installed inside the engine but also exposed and installed as an exhaust nozzle outside the engine.
FIGS. 3A and 3B are diagrams showing a constitution of a conventional lobe mixer, FIG. 3A is a side view, and FIG. 3B is a sectional view in line III—III, showing a jet port of the lobe mixer. As shown in the drawing, the lobe mixer uses longitudinal eddy generated in an exit of the lobe mixer to promote mixture of a high-speed inner flow which passes inside the mixer with a low-speed outer flow which flows outside the mixer.
The above-described lobe mixer is one effective means for reducing the jet noise. However, in the lobe mixer, vibration (forced vibration and self-excited vibration) is easily generated by a pressure difference of inner and outer surfaces, and a vibration mode is generated involving high stress and displacement in a part of the lobe mixer. In a worst case, there is a possibility that the lobe mixer is cracked, and there has been a problem that it is difficult to establish both long life and noise reduction.